FIG. 1 shows a construction of a conventional RAKE receiver. As shown, assuming that signals received from various paths and antennas are entered through independent paths, each finger controls each of the signals.
Radio frequency analog signals received by the M′-number of antennas 100 are converted into baseband digital signals at a RF analog to baseband digital converter 110. Then, the converted signals are inputted into a signal searcher 120 and a signal controller 130, respectively. The signal searcher 120 searches the intensity of the received signals and then informs the result to the signal controller 130 and fingers 140, respectively. Meanwhile, the signal controller 130 sends the signals received by the M′-number of antennas 100 to the fingers 140, one by one, according to information from the signal searcher 120.
In the above-mentioned conventional RAKE receiver, the complexity of the fingers becomes increased linearly depending on the number of the signal paths to be combined since one finger processes a single signal. Thereby, if the number of the signal paths is increased in order to increase the performance of the receiver, there arises a problem that the complexity of the receiver is further severe.
As one option to solve these problems, there has been proposed a thesis “A RECEIVER OF SIMPLE STRUCTURE FOR ANTENNA ARRAY CDMA SYSTEMS” by J. Choi, IEEE Trans. Vehic. Techn, Vol 48, No. 5, pp 1332-1340, 1999, which discloses that signals from various antennas and signals received via various paths are processed by only one finger. In the proposed receiver, when the signals are processed, they are processed at a time using time-space two-dimensional filtering scheme. However, there is a problem that the amount of calculation is increased since the coefficients of the filters must be calculated every symbols.